1. Department of Chemistry, Box 90346, Duke University, Durham, North Carolina 27708-0346, U. S. Army Research Laboratory, Materials Division, Building 4600, Aberdeen Proving Ground, Maryland 21005, Center for Neutron Research, National Institute of Standards and Technology, REACT E151, Gaithersburg, Maryland 20899, and U. S. Army Research Office, Chemical Sciences Division, P.O. Box 12211, Research Triangle Park, North Carolina 27709-2211